(a) Technical Field
Embodiments of the present inventive concept relate to a DC-DC converter, and a driving device of a light source for a display device using the same.
(b) Discussion of Related Art
A liquid crystal display (LCD) is a flat panel display (FPD), which is composed of two display panels on which field generating electrodes such as pixel electrodes and a common electrode are formed, and a liquid crystal layer interposed between the two display panels. Voltages are applied to the field generating electrodes to generate an electric field over the liquid crystal layer, and the alignment directions of liquid crystal molecules of the liquid crystal layer are adjusted by the electric field. The adjustment of the liquid crystal molecules changes the polarization of incident light, thereby enabling images to be displayed.
Since such a liquid crystal display is not self-emissive, a separate light source is required. The light source may be an artificial light source or a natural light source. The artificial light source used in the liquid crystal display may include a light emitting diode (LED), a cold cathode fluorescent lamp (CCFL), or an external electrode fluorescent (EEFL).
When using the fluorescent lamp, power consumption is large and element characteristics of the liquid crystal display may deteriorate due to heat. Further, the fluorescent lamp may be easily damaged by slight impacts. Moreover, since the temperature of a fluorescent lamp is not uniform, different sections of the lamp may have a varying luminance. Accordingly, the display quality of the liquid crystal display may deteriorate due to use of the fluorescent lamp.
The light emitting diode (LED) is a semiconductor element that has a long lifespan, a fast lighting speed, and low power consumption. Further, the LED can withstand certain impacts. Accordingly, there is a trend to include the light emitting diode (LED) in a backlight of a medium-sized or a large-sized liquid crystal display such as for a monitor or a television or in a backlight of a small-sized liquid crystal display such as for a portable phone.
The light emitting diode (LED) is driven by a DC voltage, as compared with the fluorescent lamp, which is driven by an AC voltage. When a light emitting diode (LED) is used as a backlight for a liquid crystal display, a DC-DC converter may be used to control the level of the DC voltage.
A boost type DC-DC converter may be used as the DC-DC converter. In the boost type, the duty ratio is increased to increase the current flowing to an output terminal. However, when the duty ratio is increased in this manner, the stress applied to components within the boost type DC-DC converter is increased, and heat is generated, which reduces the lifespan of the corresponding components. Further, a ripple of the current may be generated based on the increased duty ratio.